1. Field of the Invention
The present invention is broadly concerned with weir apparatus for low cost surge and flow control, particularly in relatively small waste water treatment plants. More particularly, it is concerned with such an apparatus which includes a lower, inboard weir plate along with a spaced, opposed weir plate of greater height and having one or more flow apertures therethrough at a level below the upper margin of the first weir plate. It has been found that a weir apparatus of this type gives excellent, "in tank" flow equalization without the need for auxiliary storage tanks and associated pumps and controls.
2. Description of the Prior Art
Typical waste water treatment plants employ a series of tanks or ponds for various operations such as aeration and sedimentation. Such systems also are designed to accommodate a given flow of water therethrough, based upon the perceived load requirements. However, past experience has shown that the only consistent characteristic of waste water flow is its inconsistency. That is to say, waste water treatment plants are very often subjected to rather extreme variations in both the strength and volume of waste water directed thereto, and this has resulted in many upsets and poor performance. As can be appreciated though, a waste water treatment plant has no control over when or in what volume it receives incoming feed. In addition, once waste water is directed to a treatment system, it is not conducive for long storage for further treatment. Solids within the waste water tend to settle out and anaerobic conditions will rapidly set in to create odor problems.
In an attempt to overcome these inherent problems, designers have sought to equalize the flow of waste water to treatment plants. This has generally involved use of equalization basins designed to hold surge quantities of waste water until they can be properly treated. Equalization basins may be designed as either in-line or side-line units. With in-line systems, all flow must pass through the equalization basin(s). This requires continual pumping at a near constant rate to the treatment processes. In side-line systems, the equalization basin(s) receive only that amount of waste water above the daily average. The overflow is then pumped back into the treatment process at a variable rate such that its addition to the general flow does not exceed the daily average.
While each of the above systems has its own advantages and disadvantages, both require additional storage basins and substantial mechanical equipment and energy inputs. While these considerations may not be controlling in the case of large treatment plants, they become critical in the case of small plants. As can be appreciated, the cost involved in providing auxiliary storage tanks and the like, along with the controls therefor, can be substantial in the case of a small waste water plant.